A vehicle is often equipped with an automatic travel direction specification system, such as an automatic parking system. A travel direction specification system (driver assistance system) fashioned as a parking system is for example designed to give steering instructions to the driver during the process of parking a vehicle in a parking space. The parking system may also be designed for an automatic steering wheel controlling, so that the driver does not himself have to operate the steering wheel while parking, and is thus further relieved of stress.
For safe operation of an automatic travel direction specification system, it is important that the travel direction specifications issued by the travel direction specification system be correctly converted into corresponding directions of travel of the vehicle. For example, a steering wheel angle specified by an automatic parking system is to be correctly converted into a corresponding wheel deflection angle of the moving vehicle. This is ensured by calibrating the parking system before its first use such that for an advantageous wheel deflection angle it outputs a steering wheel angle adapted thereto.
As a rule, it is assumed that the conversion of a steering wheel angle set at the steering wheel into an executed wheel deflection angle (steering wheel angle conversion) will remain constant during operation of a vehicle. Therefore, a post-calibration of the steering wheel angle conversion usually does not take place. However, the steering wheel angle conversion may change significantly during operation of the vehicle. Even slight contact of a wheel of the vehicle with a curb may for example result in track displacement and thus in a changed steering wheel angle conversion. Potholes in a street may also permanently change the mechanics of the steering wheel angle conversion. Thus, during use of a vehicle there is a high probability that changes will occur in the steering wheel angle conversion. In particular, larger deviations between a steering wheel angle conversion before operation of the vehicle and a current steering wheel angle conversion present a potential source of errors during operation of the parking system.
The problem described in the foregoing paragraph relating to the example of a parking system occurs correspondingly in other automatic vehicle direction specification systems.
U.S. Patent Application Publication No. 2007/0213901 describes a system and a method for adapting an executed wheel deflection angle of a vehicle to a target steering wheel angle specified via a positioning of the steering wheel. Here, the wheel deflection angle of at least one wheel of the vehicle is determined on the basis of a measured yaw rate, and is compared to the target wheel deflection angle. If a deviation is determined between the wheel deflection angle and the target wheel deflection angle, at least one wheel of the vehicle is correspondingly adjusted.
However, at low vehicle speeds the yaw rate of a vehicle can be determined only imprecisely. Therefore, the system and the method described in U.S. Patent Application Publication No. 2007/0213901 are poorly suited for parking a vehicle in a parking space. It is therefore desirable to provide a more reliable possibility for determining an item of travel direction information for a vehicle.